Many scanning devices are configured of a plurality of lenses of uniform diameter juxtaposed linearly, and a plurality of light-receiving elements aligned in the same direction. In a scanning device configured with a plurality of lenses, pixel values for a row of pixels change in regular periods corresponding to the spacing of the lenses due to the focusing properties of the lenses. Hence, white reference data acquired by this type of scanning device does not change linearly, but rather cyclically in intervals corresponding to the lens spacing.